Lithography methods, methods for forming patterning tools and patterning tools

ABSTRACT

Methods of lithography, methods for forming patterning tools, and patterning tools are described. One such patterning tool include an active region that forms a first diffraction image on a lens when in use, and an inactive region that forms a second diffraction image on a lens when in use. The inactive region includes a pattern of phase shifting features formed in a substantially transparent material of the patterning tool. Patterning tools and methods, as described, can be used to compensate for lens distortion from effects such as localized heating.

PRIORITY APPLICATION

This application is a divisional of U.S. application Ser. No.13/214,865, filed Aug. 22, 2011, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

Various embodiments described herein relate to apparatus, systems, andmethods associated with lithography, for example reticles and methodsfor using reticles in the manufacture of semiconductor components.

BACKGROUND

Photolithography is a fabrication technique that is employed for use ina number of industries, including the semiconductor processing industry.Specifically, photolithography exposes energy, such as ultraviolet (UV)light, x-ray wavelength, other wavelengths of radiation, etc. toselected regions of a surface. In one common technique, the surfaceincludes a semiconductor wafer such as silicon that has been coated witha resist material. The resist material properties are locally changedwhen exposed to the energy source, which allows selected regions of theresist material to remain, while unwanted regions of the resist materialare removed.

In one method of photolithography, a pattern of features is formed on apatterning tool, such as a reticle or mask, (a patterning tool isreferred to hereinafter in the specification by example as a “reticle”)and energy transmitted through the pattern on the reticle is focusedonto a working surface to print functionally important features on theworking surface using a lens that adjusts the scale of the pattern onthe reticle to fit the working surface. In the semiconductor industry,there is an ever present pressure to reduce the size of features in thepattern to increase the density of printed features packed into the samesemiconductor surface area. In one example industry, manufacturers ofmemory chips such as dynamic random access memory (DRAM) or flash memorystrive to put more storage cells onto a single chip.

As feature size decreases, photolithography of smaller and smallerfeatures becomes more and more difficult. Imaging fidelity can bedegraded by some non-ideal properties of a lens, such as aberrations.During high volume manufacturing, a lens constantly receives energy andlens heating may cause optical aberrations. Methods and devices toreduce lens heating induced optical aberrations are needed to keep pacewith ever increasing photolithography demands such as smaller featuresizes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a photolithography system according to the prior art.

FIG. 2 shows a side view of a lens according to an embodiment of theinvention.

FIG. 3 shows a top view of the lens from FIG. 2 according to anembodiment of the invention.

FIG. 4A shows a heat map and a top view of the lens from FIG. 2according to an embodiment of the invention.

FIG. 4B shows a block diagram representation of a reticle, according toan embodiment of the invention.

FIG. 5 shows a cross section representation of a reticle according to anembodiment of the invention.

FIG. 6A-6G show processing steps in forming a reticle according to anembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings that form a part hereof and in whichare shown, by way of illustration, specific embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and logical, electricalchanges, etc. may be made.

The term “horizontal” as used in this application is defined as a planeparallel to the conventional plane or surface of a substrate, such as awafer, die, or reticle, regardless of the orientation of the substrate.The term “vertical” refers to a direction perpendicular to thehorizontal as defined above. Prepositions, such as “on”, “side” (as in“sidewall”), “higher”, “lower”, “over” and “under” are defined withrespect to the conventional plane or surface being on the top surface ofthe substrate, regardless of the orientation of the substrate. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, along with the full scope of equivalents towhich such claims are entitled.

FIG. 1 shows a system where a pattern of features is formed on a reticleand the pattern is then transferred to a working surface byphotolithography. In one embodiment the pattern of features transferredto the working surface includes semiconductor device component features,including, but not limited to, source/drain regions, transistor gates,trace lines, source/drain contacts, vias, capacitor plates, etc. FIG. 1shows a photolithography system 100 according to an embodiment of theinvention. The system 100 can operate on a substrate 110. In oneembodiment, the substrate 110 includes a semiconductor substrate, suchas a silicon wafer. Although a semiconductor substrate is discussed forillustration, embodiments of the invention will comprise other workingsurfaces utilizing photolithography.

A resist material 120 is located over a surface of the substrate 110. Areticle 130 is shown with a substantially transparent region (shown asan opening 132), and is spaced apart from the resist material 120 by anoptical system. The reticle 130 is shown in a simplified form with anenergy blocking region and an opening 132 in the energy blocking region.Although depicted in FIG. 1 as an opening 132, in one embodiment, thesubstantially transparent region can comprise a material such as glassor quartz. In one embodiment, the energy blocking region of the reticle130 includes an energy blocking (e.g., opaque) material, such as chrome,adapted to block a portion of energy 140 being transmitted from anenergy source and/or an attenuating (e.g., partly opaque) material, suchas molybdenum silicide, adapted to phase shift a portion of the energy140. The terms “transparent”, “attenuated”, “partly opaque” and otherassociated optical terms in the present specification refer to opticalproperties of the reticle 130. In one embodiment, examples ofsubstantially transparent materials transmit greater than 99 percent ofincident energy. In one embodiment, examples of substantially opaquematerials block greater than 99 percent of incident energy. In oneembodiment, examples of attenuating materials transmit between 1 and 99percent of incident energy. Possible energies used in the processinclude, but are not limited to, UV radiation and x-ray radiation. Onesource of suitable energy is from a laser light source.

An energy source (not shown) transmits energy 140 toward the resistmaterial 120, with a portion of the energy 140 being blocked by thereticle 130. A portion of the energy 140 is shown as being transmittedthrough the opening 132 in the reticle 130 and toward a lens 150 ofprojection optics (although only one lens is shown in FIG. 1, projectionoptics may comprise, for example, up to and in some cases more than 40lenses). A lens 150, may be used to focus and/or scale the energy 140transmitted through the reticle 130, thus allowing focused and/or scaledenergy 145 to print smaller features onto the resist material 120 thanmight be possible using just a reticle 130. The focused and/or scaledenergy 145 is shown contacting the resist material 120 in a selectedregion 122. The focused and/or scaled energy 145 interacts with theresist material 120 in the selected region 122 to selectively alter theproperties of the resist material 120 in the selected region 122. Twopossible alterations include a curing of the resist material and aweakening of the resist material. In one possibility, the resistmaterial 120 in the selected region 122 is cured and remains while thenon-selected region of the resist material 120 is removed. In anotherpossibility, the resist material 120 in the selected region 122 isweakened and is removed while the non-selected region of the resistmaterial remains.

FIG. 2 shows another side view of incident energy 140 interacting with alens 150 to provide focused and/or scaled energy 145 similar to thediagram of FIG. 1. FIG. 2 further shows regions 210 of local heating ofthe lens 150 that can distort the shape of the lens 150, and produce adistorted energy pattern 146.

FIG. 3 shows a top view of a lens 150, including the regions 210 oflocal heating. In one example, the regions 210 of local heating areproduced by optical diffraction of a pattern in a reticle, such asreticle 130 from FIG. 1. FIG. 3 also shows regions 212 of the lens 150.When regions 212 are also heated along with regions 210, distortion inthe lens 150 due to heating in regions 210 can be (at least partially)compensated, and optical aberrations reduced compared to only heatingregions 210.

FIG. 4A shows a heat map 402 measured on a lens 150 when performing alithography operation. The heat map 402 includes a pattern of zerothorder live pattern diffraction images 410. The zeroth order live patterndiffraction images 410 map to regions 210 of the lens 150, and bythemselves, result in unwanted lens distortion. FIG. 4 further shows apattern of first order sub-resolution fill (SRF) diffraction images 420,and second order SRF diffraction images 430. In the example shown, thefirst order SRF diffraction images 420 map to regions 212 of the lens150. The addition of the first order SRF diffraction images 420 providecompensating heating from local heating in the lens 150 from the firstorder live pattern diffraction images 410. In other embodiments, otherdiffraction images, such as second order diffraction images 430 mayprovide compensating heating from local heating in the lens 150 from thefirst order live pattern diffraction images 410.

FIG. 4B shows an example reticle 440 according to an embodiment of theinvention. The reticle 440 includes first regions 442 and second regions444. In one example, the first regions 442 are active regions that areused to form the pattern of live pattern diffraction images used toprint functionally important features on the working surface (e.g.,device features such as transistors and electrical transmission lines).In one example, the second regions 444 are inactive regions of thereticle 440, which are used to form a pattern of SRF diffraction images(which will not print a feature on the working surface) and/or a patternof other images that will print functionally unimportant features on theworking surface (e.g., images that will print so called “dummy” featureson the working surface). In one example, the pattern of zeroth orderlive pattern diffraction images 410 from FIG. 4A are formed frominteraction with the first regions 442. In one example, the pattern offirst order SRF diffraction images 420 are formed from interaction withthe second regions 444.

In one example, the second regions 444 are configured with diffractiongratings or similar features that are oriented to direct diffractedenergy (e.g., light) of an order (e.g., first order, second order, thirdorder, etc.) to regions 212 of lens 150 that at least partiallycompensate for heating in regions 210 of the lens that results fromtransmitting energy through the first regions 442. In one example, thefeatures in the second regions are formed as sub-resolution features.Sub-resolution features will not print on a working surface, howeverthey will allow a portion of incident energy to diffract, and heatregions 212.

As devices, such as semiconductor devices, become more efficient intheir layout, less real estate is available for second regions 444. Inone example, the second regions 444 are less than approximately 27percent of the area of the reticle 440. In one example, the secondregions 444 are less than approximately 11 percent of the area of thereticle 440.

FIG. 5 shows a cross section of a reticle 500 similar to reticle 440,from FIG. 4B. The reticle 500 includes a first region 502 that is anactive region similar to regions 442, and a second region 504 that is aninactive region similar to regions 444. FIG. 5 illustrates a firstreticle material 510, a second reticle material 512, and a third reticlematerial 514. In one example, the first reticle material 510 issubstantially transparent. In one example, the first reticle material510 includes a silicon dioxide glass or quartz substrate. In oneexample, the second reticle material 512 includes a layer of attenuatingmaterial. In one example, the second reticle material 512 includesmolybdenum silicide. In one example, the third reticle material 514includes a layer of energy blocking material, such as a substantiallyopaque layer. In one example, a substantially opaque material blocksgreater than 99 percent of incident energy. In one example, the thirdreticle material 514 includes chrome.

Various portions of the reticle materials 510, 512, and 514 have beenremoved to form a pattern of features for lithography. For example, thesecond reticle material 512 is patterned to form features 522. In oneexample, the features 522 include phase shifting features. The thirdreticle material 514 is patterned to form features 524. In one example,the features 524 block substantially all (e.g. 99 percent or more)transmission of energy through the reticle 500. The first reticlematerial 510 is patterned to form features 520. In one example, thefeatures 520 include phase shifting features.

Less efficient configurations may use an attenuating layer, such as thesecond reticle material 512, to form features in the second region 504of the reticle 500. In the example shown in FIG. 5, all of the featuresin the second region 504, including features 520, are formed in asubstantially transparent first reticle material 510. As a result, ahigher amount of energy can be transmitted through the reticle 500 inthe second region 504 as compared to an embodiment where the features520 are formed in an attenuating material.

Using configurations shown in FIG. 5 and FIG. 4B, the second regions 444can be made smaller as a percentage of the area of reticle 440, whiletransmitting the same amount of energy through the reticle to providecompensation to the lens. Alternatively, the second regions 444 cantransmit more energy through the reticle to provide a greatercompensating effect to the lens, while using the same percentage of thearea of reticle 440. Using configurations shown in FIG. 5 and FIG. 4B,in one example, the second regions 444 are less than approximately 27percent of the area of the reticle 440. In one example, the secondregions 444 are less than approximately 11 percent of the area of thereticle 440.

FIGS. 6A-6F illustrate an example method of forming a reticle, accordingto an embodiment of the invention. In FIG. 6A, a second reticle material512 is formed over a first reticle material, and a third reticlematerial 514 is formed over the second reticle material 512. Asdiscussed above, in one example, the first reticle material 510 issubstantially transparent. In one example, the first reticle material510 comprises silicon dioxide glass or quartz, for example. In oneexample, the second reticle material 512 comprises an attenuating layer.In one example, the second reticle material 512 comprises molybdenumsilicide. In one example, the third reticle material 514 comprises asubstantially opaque layer. In one example, the third reticle material514 comprises chromium (e.g., a layer of chrome). FIG. 6A shows a firstregion 600A and a second region 600B. In one example, the first region600A comprises an active region, and the second region 600B comprises aninactive region.

FIG. 6B shows an operation where a first resist 602 is formed on thethird reticle material 514, and a pattern of features 604 is formed inthe first resist 602. FIG. 6C shows an operation where the pattern offeatures 604 is used to remove material from the second reticle material512 and the third reticle material 514 to form spaces 606 and 608. Afterthe formation of spaces 606 and 608, the first resist 602 is removed.

In FIG. 6D, a second resist 610 is formed only over the first region600A, filling spaces 606, but leaving spaces 608 open to expose portionsof the first reticle material 510. In FIG. 6E, the spaces 608 are usedto pattern and form spaces 612 in the first reticle material 510 withinthe second region 600B of the reticle 600. In one example, the spaces612 form sub-resolution phase shifting features in the first reticlematerial 510. After the spaces 612 are formed in the first reticlematerial 510, the portions of the second reticle material 512 and thethird reticle material 514 not protected by the second resist 610 areremoved. In one example, the second reticle material 512 and the thirdreticle material 514 are removed in a single processing operation byremoving the second reticle material 512. In one example, the secondreticle material 512 and the third reticle material 514 are removedusing two material specific removal processes such as etchingoperations. After the spaces 612 are formed in the first reticlematerial 510, and the portions of the second reticle material 512 andthe third reticle material 514 not protected by the second resist 610are removed, the second resist 610 is removed.

FIG. 6F shows a third resist 614 covering a portion of the first region600A of the reticle 600. In FIG. 6F, the third resist 614 is used toprotect region 616 within the first region 600A, leaving region 617exposed to further processing. In FIG. 6G, a portion 618 of the thirdreticle material 514 is removed from within the region 617 leftunprotected by the third resist 614. A portion 609 of the second reticlematerial 512 is left behind within the region 617 left unprotected bythe third resist 614. In one example, the removal of the portion 618while leaving the portion 609 is accomplished with a material selectiveetch.

The resulting reticle 600 includes an active region 600A with features622 that are phase shifting features, and features 620 that are energyblocking features. The combination of phase shifting features 622 andenergy blocking features 620 in the active region 600A provides multiplelithography tools to sharpen and otherwise enhance functionallyimportant features printed on a working surface. At the same time, theresulting reticle 600 includes an inactive region 600B with features 624formed from a single reticle material 510. In examples where the singlereticle material 510 is substantially transparent, a high transmissionof energy is passed through the inactive region 600B, while maintainingthe ability of features 624 to diffract and direct energy to portions ofa lens for a compensating effect.

While a number of embodiments of the invention are described, the abovelists are not intended to be exhaustive. Although specific embodimentshave been illustrated and described herein, it will be appreciated bythose of ordinary skill in the art that any arrangement that iscalculated to achieve the same purpose may be substituted for thespecific embodiment shown. This application is intended to cover anyadaptations or variations of the present invention. It is to beunderstood that the above description is intended to be illustrative andnot restrictive.

Combinations of the above embodiments, and other embodiments, will beapparent to those of skill in the art upon studying the abovedescription.

What is claimed is:
 1. A method, comprising: transmitting energy througha first region of a patterning tool, forming a first diffraction imageon a lens while forming a pattern of features on a working surface;transmitting energy through a second region of the patterning tool,forming a second diffraction image on the lens, wherein the secondregion of the patterning tool includes a pattern of features that areformed in a substantially transparent material of the patterning tool;wherein lens distortion from local heating of the lens due to the firstdiffraction image is at least partially compensated by local heating ofthe lens due to the second diffraction image.
 2. The method of claim 1,wherein transmitting energy through the second region comprisestransmitting light through a pattern of phase shifting features formedin quartz.
 3. The method of claim 1, wherein transmitting energy throughthe second region comprises transmitting light through a pattern ofsub-resolution features formed in the substantially transparentmaterial.
 4. The method of claim 1, wherein transmitting energy throughthe second region comprises transmitting light through a pattern ofsub-resolution features formed only in the substantially transparentmaterial.
 5. The method of claim 1, wherein the lens distortion fromlocal heating of the lens due to the first diffraction image is at leastpartially compensated by local heating of the lens due to a first orderpattern in the second diffraction image.
 6. The method of claim 1,wherein forming a pattern of features on a working surface comprisesforming a pattern of semiconductor device features on a substrate. 7.The method of claim 1, wherein transmitting energy through the firstregion of the patterning tool comprises transmitting light through apattern of features formed in an attenuating material of a reticle. 8.The method of claim 1, wherein transmitting energy through the firstregion of the patterning tool comprises transmitting light through apattern of partially opaque features.
 9. The method of claim 1, whereintransmitting energy through the first region of the patterning toolcomprises transmitting light through a region that includes molybdenumsilicide features.
 10. The method of claim 1, wherein transmittingenergy through the first region of the patterning tool comprisestransmitting light through a region that includes chrome features. 11.The method of claim 1, wherein transmitting energy through the firstregion of the patterning tool comprises transmitting light through aregion that includes phase shifting features.
 12. A method, comprising:transmitting energy through a first region of a patterning tool, forminga first diffraction image on a lens while forming a pattern of featureson a working surface; transmitting energy through a second region of thepatterning tool that transmits more energy than the first region of thepattering tool, forming a second diffraction image on the lens; whereinlens distortion from local heating of the lens due to the firstdiffraction image is at least partially compensated by local heating ofthe lens due to the second diffraction image.
 13. The method of claim12, wherein transmitting energy through a second region of thepatterning tool includes transmitting energy through a region that isless than approximately 27 percent of a total area of the patterningtool.
 14. The method of claim 12, wherein transmitting energy through asecond region of the patterning tool includes transmitting energythrough a region that is less than approximately 11 percent of a totalarea of the patterning tool.
 15. The method of claim 12, whereintransmitting energy through a second region of the patterning toolincludes transmitting energy through a substantially transparent regionof the patterning tool.
 16. The method of claim 15, wherein transmittingenergy through the second region comprises transmitting light throughquartz.
 17. The method of claim 12, wherein transmitting energy throughthe second region comprises transmitting light through a pattern ofphase shifting features.
 18. The method of claim 12, whereintransmitting energy through the second region comprises transmittinglight through a pattern of sub-resolution features.
 19. The method ofclaim 12, wherein the lens distortion from local heating of the lens dueto the first diffraction image is at least partially compensated bylocal heating of the lens due to a first order pattern in the seconddiffraction image.